This invention relates generally to radio communication systems and, in particular, to antennas that can be built into portable terminals in such systems and that enable such terminals to communicate in several frequency bands.
The cellular telephone industry has made phenomenal strides in commercial operations in the United States as well as the rest of the world. Growth in major metropolitan areas has exceeded expectations and outstripped system capacities. Important aspects of the advance of radio communication systems like cellular telephone systems are a change from analog to digital transmission and selection of an effective digital transmission scheme. Current and planned digital radio telephone communication systems use frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and combinations of these.
To help ensure compatibility of equipment made by many manufacturers, many communication systems are defined by standards published by standards-setting organizations. For example, analog cellular telephone communication systems follow standards such as the Advanced Mobile Phone System (AMPS) and the Nordic Mobile Telephone (NMT) system, and digital systems follow standards such as TIA/EIA-136 that is published by the Telecommunications Industry Association and is now called simply TDMA, and the Global System for Mobile (GSM) that is now published by the Third Generation Partnership Project (3GPP).
One of the parameters specified by the various standards is the frequency band or bands used for control and information signals. For example, TDMA systems in the U.S. operate in frequency bands near 800 MHz and/or 1900 MHz, and GSM systems operate in frequency bands near 900 MHz and/or 1800 MHz.
A device like a handheld cellular telephone sends and receives radio signals in these frequency bands with an antenna that can take a number of different forms. (The antenna has a resonance frequency in the frequency band of interest.) For example, rod or whip antennas have been common, but have fallen from favor as cellular telephones have become smaller and have had to handle multiple frequency bands. Helical antennas have become more common since they are suited to high frequency applications where an antenna""s length is to be minimized and since they can handle multiple frequency bands. For example, a small, non-uniform, helical, dual-band antenna is disclosed in commonly assigned U.S. Pat. No. 6,112,102 to Ying for xe2x80x9cMultiple Band Non-Uniform Helical Antennasxe2x80x9d.
Even so, demand for handheld devices that are smaller and that can communicate in more than one frequency band has led to the design of new antennas that can be xe2x80x9cbuilt inxe2x80x9d to the devices, which is to say that the outline of a device does not reveal the antenna in the way that a rod or whip antenna would be revealed. Devices having built-in antennas are described in U.S. Pat. No. 5,929,813 to Eggleston and its continuations.
Commonly assigned U.S. Pat. No. 6,166,694 to Ying for xe2x80x9cPrinted Twin Spiral Dual Band Antennaxe2x80x9d and U.S. patent application Ser. No. 09/112,366 by Ying for xe2x80x9cMiniature Printed Spiral Antenna for Mobile Terminalsxe2x80x9d describe small, built-in, multi-frequency-band antennas. As depicted in FIG. 3 of the ""694 patent, which is incorporated in this application by reference, such an antenna may include two spiral conductor arms that have different lengths and that are mounted on a dielectric substrate that is itself mounted on a printed circuit board (PCB). Also as described in the ""694 patent, electrical connections between the spiral arms and the circuit board are made by antenna feed and ground pins.
An electrically sensitive part of an antenna such as that described by Ying is its feed arrangement or connectors to the printed circuit board. FIGS. 1A, 1B depict one such arrangement in cross-section. A patch 101, which may include spiral arms and a dielectric substrate as described in the ""694 patent, can be connected to a circuit board 103 by feed and ground terminals 105, 107 that depend from the patch 101 and are intended to make electrical contact with respective pads 109, 111 on the board 103. The patch 101 may be mounted on an exterior cover of the device such that assembly of the cover and the case of the device brings the terminals 105, 107 into physical contact with the pads 109, 111.
Besides simply needing to ensure that the terminals and pads are in contact when the device is assembled, it is usually important to maintain a predefined geometry of the feed and ground terminals in order to keep an accurate resonance frequency of the antenna. One way this has been done includes forming the terminals 105, 107 as J-shaped legs from the patch 101 itself, but the accuracy of the terminal geometry depends almost entirely on highly precise dimensions of the J-legs and minimal deflection of the J-legs from their nominal positions.
Excessive deflection and/or failure to connect can be caused by improper positioning of the patch 101 with respect to the board 103 in x, y, and z directions. As depicted in FIG. 1A, the patch and board are mutually displaced in the x-direction indicated by the arrow to such an extent that the terminals 105, 107 and pads 109, 111 fail to make contact. In FIG. 1B, the patch and board have been displaced in the z-direction indicated by the arrow to such an extent that the terminals have been deformed. Even if displacement in the other directions could establish contact between the terminals and pads, the geometry of the feed arrangement would be inaccurate, affecting communication performance of the antenna.
Although it is desirable from a cost perspective to attach such a patch to the cover of a device like a cellular phone, good assembly tolerances and hence proper connection geometry are difficult to ensure using typical manufacturing methods.
This invention overcomes the problems described above at little or no extra cost with feed arrangements of antennas for mobile phone handsets, etc., that include combinations of connection pin design, sideways spring forces, and mating holes or cavities in the mating circuit boards.
In one aspect of the invention, an antenna has a patch radiating element having a feed terminal and a ground terminal that extend from the patch radiating element, and a circuit board that is electrically connected to the patch radiating element by the feed and ground terminals after the antenna is assembled. The circuit board has respective areas for electrically contacting the feed and ground terminals that accommodate displacement of the patch radiating element with respect to the circuit board as the antenna is assembled.
In further aspects, the respective contacting areas may be holes, and the feed and ground terminals may be formed as J-shaped legs from the patch radiating element and may exert respective spring forces against respective contacting areas when the antenna is assembled. The feed and ground terminals may extend into the respective contacting areas after the antenna is assembled, and the distance between the contacting areas may be about five millimeters, and each contacting area may be about two millimeters wide.
The contacting areas may be holes that are through-plated with a metal and that mechanically guide the feed and ground terminals to the circuit board as the antenna is assembled. The patch radiating element and the feed and ground terminals may be punched out of a sheet of a conductive material, with the sheet being about 0.15 millimeter thick and each of the feed and ground terminals being about ten millimeters long and bent substantially perpendicular from the patch radiating element before the antenna is assembled. The feed and ground terminals may be punched from the patch radiating element and have curved cross-sections, and the feed and ground terminals may be attached to the patch radiating element such that the feed and ground terminals engage the contacting areas, respectively, as the antenna is assembled.
In another aspect, an antenna has a radiator mounted on a substrate, at least two terminals that are connected to the radiator and that extend away from a surface of the substrate, and a circuit board that is electrically connected to the radiator via the terminals. The terminals are accommodated by respective holes in the circuit board and are resilient. In this way, mis-alignment between the substrate and the circuit board is compensated, reducing the risk of antenna frequency offset.
The terminals may be formed as J-shaped legs from the radiator, and may exert respective spring forces against sides of the respective holes when the antenna is assembled. The distance between the holes may be about five millimeters, and each hole may be about two millimeters wide.
The radiator and the terminals may be punched out of a sheet of a conductive material that is about 0.15 millimeter thick, and each of the at least two terminals may be about ten millimeters long and be bent substantially perpendicular from the radiator before the antenna is assembled. The terminals also may have curved cross-sections.